I remember seeing a World War II movie around 1964. The movie is about allied planes that had to bomb a dam. The trick was the planes had to come in only at a certain angle and height to drop the bomb, to be able to damage the dam. Maybe Cliff robertson was in it? Trying to find the title.
The Dam Busters”(1955)
http://www.imdb.com/title/tt0046889/
Some details also fit…
http://www.imdb.com/title/tt0057811/